S/2004 S 4

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S/2004 S 4

Discovery
Discovered by	Joseph Spitale / Cassini Imaging Science Team.[1]
Discovered on	21 June 2004
Orbital characteristics
Semimajor axis	~140,100 km.[2]
Eccentricity	unknown, small
Orbital period	~0.618 d [2]
Inclination	unknown, small
Is a satellite of	Saturn
Physical characteristics
Mean diameter	3-5 km
Rotation period	probably synchronous
Axial tilt	unknown
Albedo	unknown
Atmosphere	none

S/2004 S 4 is the provisional designation of an unconfirmed object seen orbiting Saturn within the inner strand of the F ring on 21 June 2004. It was spotted while J. N. Spitale was trying to confirm the orbit of another provisional object, S/2004 S 3 that was seen 5 hours earlier just exterior to the F ring.^[1] The announcement was made on September 9, 2004.^[3]

Despite later attempts to recover it, it has not been reliably sighted since. Notably, an imaging sequence covering an entire orbital period at 4 km resolution taken on 15 November 2004 failed to recover the object. This suggests that it was a temporary clump of material that had disappeared by that time.^[4]

An interpretation where S3 and S4 are or were a single object on a F-ring crossing orbit is also possible.^[3] Such an object might also be orbiting at a slightly different inclination to the F ring, thereby not actually passing through the ring material despite being seen both radially inward and outward of it.

If a solid object after all, S/2004 S 4 would be 3−5 km in diameter based on brightness.

[edit] References

1. ^ ^{a b} Martinez, C.; Ormrod, G.; and Finn, H.; Cassini-Huygens Press Releases: Cassini Discovers Ring and One, Possibly Two, Objects at Saturn September 9, 2004
2. ^ ^{a b} PGJ Astronomie webpage (Gilbert Javaux) Note that the F ring is centered at ~140,180 km
3. ^ ^{a b} IAUC 8401: S/2004 S 3, S/2004 S 4, and R/2004 S 1 2004 September 9 (discovery)
4. ^ Spitale, J. N.; et al. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692. doi:10.1086/505206. 

v • d • e Moons of Saturn Generally listed in increasing distance from Saturn. Temporary names in italics. Ring shepherds moonlets · Pan · Daphnis · Atlas · Prometheus ·  ?S/2004 S 6 · ?S/2004 S 4 · ?S/2004 S 3 · Pandora Co-orbitals Epimetheus · Janus Inner large (and Trojan) Mimas · Methone · Anthe · Pallene · Enceladus · Tethys (Telesto • Calypso) · Dione (Helene • Polydeuces) Outer large Rhea (rings) · Titan · Hyperion · Iapetus Inuit group Kiviuq · Ijiraq · Paaliaq · Siarnaq · Tarqeq Norse group Phoebe · Skathi · S/2007 S 2 · Skoll · S/2004 S 13 · Greip · Hyrrokkin · Mundilfari · Jarnsaxa · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2007 S 3 · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot Gallic group Albiorix · Bebhionn · Erriapus · Tarvos Rings of Saturn · Cassini-Huygens · Themis · Chiron